Exam Question

### A. Introduction and Principle of Operation
An Exhaust Gas Boiler (EGB), also known as a Waste Heat Recovery Boiler, is a critical component for improving the overall thermal efficiency of a marine propulsion plant. Its primary function is to utilize the considerable thermal energy present in the main engine's exhaust gases, which would otherwise be lost to the atmosphere, to generate low-pressure saturated steam. This steam is then used for various auxiliary services onboard, such as fuel oil heating, cargo heating, domestic services, and purifier heating.
To ensure a continuous supply of steam, especially when the main engine is stopped or at low load (e.g., in port or during maneuvering), many vessels are fitted with a **Composite Boiler**. As described in the provided context, a composite boiler is a dual-purpose unit that can generate steam using either the main engine exhaust gas or a separate oil-fired burner, or both simultaneously. This design provides operational flexibility and ensures steam is available regardless of the main engine's operational status.
A common example is the vertical smoke-tube type, such as the Cochran boiler, which offers a compact and robust design.